A hydrophilic colloid, such as gelatin, is one of the major components of a photographic emulsion. There a numerous features that gelatin contains that make it a desirable material for use in this type of application. Gelatin is water soluble and can be coated from an aqueous solution. It contains chemical sites that may be crosslinked, that leave the coated product with a sufficient durability. Additionally, the gelatin is hydrophilic, and thus, it will allow developer solutions to penetrate and diffuse into the photographic material when processed using an aqueous processing composition. Each of these features are important to the success and performance of the photographic product.
Gelatin can be coated from an aqueous solution. One of the parameters to control is the Theological properties or viscosity of the solution. When a gelatin solution is prepared, the Theological properties can be modified by the use of certain polymeric additives or thickeners. One standard thickener used for photographic packages is polystyrene sulfonate.
Once a gelatin coating is prepared, chemical hardening is critical. It is the chemical hardening that renders the coating insoluble, and provides the required durability. Chemical hardening of gelatin can be carried out by various means. Hardeners can be either inorganic or organic in nature. A typical inorganic hardening agent is Ca.sup.++ or other divalent cations. Typical organic species are aldehyde, s-triazines, epoxides, isocyanates, active olefins and sulfone based hardeners to name a few P. I. Rose, The Theory of Photographic Process, 4th Edition, edited by T. H. James (Macmillan Publishing Company, New York, 1977) p. 51-65!. Vinyl-sulfone hardeners are used to harden gelatin in the manufacture of photographic products various layers of the product. The use of vinyl-sulfones as hardeners in photographic elements is described in, for example, U.S. Pat. Nos. 3,642,486, 3,841,872, 4,670,377, 4,897,344, 4,975,360 and 5,071,736. Of particular interest are 1,2-bis(vinyl-sulfonyl)methane (BVSM), 1,2-bis(vinyl-sulfonyl)methane ether (BVSME) and 1,2-bis(vinyl-sulfonyl acetoamide) ethane (BVSAE).
The use of polymeric hardeners in a gelatin system has been reported in the literature. See D. M. Burness and J. Pouradier, 1987 (The Theory of Photographic Process, 4th Edition, edited by T. H. James Macmillan Publishing Company, New York, 1977, p. 84) which discloses several polymers that are active hardeners, e.g. particularly acetylated cellulose, copolymers of glycidyl acrylates, amino polymers containing chlorotriazine pendant groups. Several polymeric hardeners containing vinyl-sulfonyl side groups have been disclosed for use in hardening gelatin. See, for example U.S. Pat. Nos. 4,161,407, 4,460,680, and 4,481,284.
Commonly assigned copending U.S. patent application Ser. No. 08/686,082, filed Jul. 24, 1996 discloses the use of certain borate compounds can enhance the hardening rate when added to a gelatin and chemical hardener solution. The use of borates aid hardening of a total gelatin package. In a multilayer package, it would be expected that the borate compounds of the -082 application will influence all layers and not be layer specific. In the above cited patent application, the use of polymeric hardeners in combination with borate compounds were used to gain layer specific hardening. Additionally, for any rheological changes, another polymer was required.